Photochemical Pretreatment Research Articles

Photochemical Pre-Treatment to Quantify Iron in Thin Films

Metal-based catalysts are indispensable in modern chemistry and one of the biggest challenges for industrial applications is to quantify their performance and stability. The metrics of performance can be obtained in terms of the turnover number and turnover frequency, and the stability might be associated with the leaching of the heterogeneous catalysts. Thus, metal quantification is the starting point to understand and evaluate the features of catalysts. Among the technologies for metal determination, spectrophotometric analysis stands out for being cheap and easy to perform. However, the challenge is the sample preparation to direct quantification from the heterogeneous materials. Herein, it is shown how important is the photochemical pre-treatment for the quantification of the total iron from heterogeneous thin films composed of iron-based materials. The photochemical approach was used to ensure a full dissociation of iron ions before the quantification. This method was revealed to be highly effective and precise, having a wide range of applications for different iron-based catalysts.

Photochemical transformation of diketone dopants in polyester matrices: Effect of dopants concentration and polyester structure on changes in molecular characteristics and hydrolysis of the matrices

Photochemical transformations of photoactive diketone derivatives, 1,2-diphenylethane-1,2-dione (benzil, BZ) and 1,4-bis(benzoylcarbonyl)benzene (bisbenzil, BIS), and the effects of their transformations on changes in the molecular characteristics and hydrolytic properties of poly(ε-caprolactone) (PCL) and polylactide (PLA) matrices are reported. Studies were performed in a broad dopant concentration range of 0.2–7.5 wt%. Structural changes were observed by FTIR spectroscopy. FTIR spectroscopy proved the progressive transformation of BZ to benzoyl peroxides and, in the case of PCL, the formation of polar groups. Changes in molecular characteristics were observed in GPC traces. Irradiation of the doped polymer films at λ > 400 nm under an air atmosphere resulted mainly in the degradation of the polymer matrices. Additionally, high dopant concentrations in PCL led to partially crosslinked structures with gel contents up to 15%. The photochemical transformation of dopants had a large impact on the PCL matrices compared to that of the PLA matrices. A subsequent hydrolysis process was investigated by determining the extractable products as well as using GPC. Hydrolysis of irradiated PCL samples showed a significant acceleration of hydrolysis compared to that of nonirradiated samples. Furthermore, the hydrolysis rate gradually increased with increasing dopant concentration. The PCL crosslinking and degradation is adjustable by the type of dopant, concentration of dopant and intensity of light during irradiation of PCL. In contrast, a photochemical pretreatment had no observable effect on the hydrolysis of PLA under the investigated conditions.

Biotreatability enhancement of aqueous Reactive Black 5 by hydrogen peroxide/ultraviolet advanced oxidation process

The efficiency of ultraviolet/hydrogen peroxide photo‐oxidation processing for enhancing the biodegradability of Reactive Black 5 prior to biological treatment processing of acclimated and non‐acclimated sequencing batch reactors was evaluated. Photo‐oxidation experiments were conducted according to an experimental design method in which aqueous Reactive Black 5 samples with an initial concentration of 200 mg/l were exposed to ultraviolet irradiation for 15, 30 and 60 min in the presence of various concentrations of hydrogen peroxide (250, 500 and 1000 mg/l) at pH 7. Pretreated samples were then subjected to respirometric biodegradability tests using the sludge cultures obtained from acclimated and non‐acclimated sequencing batch reactors for the determination of the kinetic constants of qmax and Ks according to the modified Organisation of Economic Cooperation and Development 209 method. Calculated values of qmax and Ks showed that the acclimated sludge of the sequencing batch reactor showed a better performance than the non‐acclimated sludge in the degradation of photochemically pretreated aqueous Reactive Black 5. The advantage of acclimated sludge compared with non‐acclimated sludge for the biodegradation of Reactive Black 5 diminished when photochemical pretreatment conditions reached higher levels in terms of oxidation time and hydrogen peroxide concentration.

Effect of photochemical pre-treatment on COD fractionation of a non-ionic textile surfactant

The work presented in this paper is focused on the effect of photochemical (H2O2/UV-C) pretreatment on COD fractionation and degradation kinetics of a non-ionic textile surfactant. In the first part of the study, the COD of non-ionic surfactant was adjusted to 1000 mg/L in order to simulate real effluent originating from the textile preparation stage featuring desizing, scouring, washing and rinsing operations. The surfactant was subjected to H2O2/UV-C pretreatment for up to 120 min at a dose of 30 mM (980 mg/L) H2O2. The biodegradability studies for untreated and photochemically treated samples were evaluated on the basis of modeling of oxygen uptake rate (OUR) profiles. Modelling of OUR profiles conducted for untreated sample showed that single complex substrate was subjected to enzymatic breakdown and disintegrated into one readily and two types of slowly biodegradable substrates. After modelling the biodegradation of photochemically pretreated sample, the readily biodegradable COD fraction was reduced, on the other hand, more slowly biodegradable organics were generated. A higher disintegration rate was obtained for chemically pretreated samples. However, other kinetic constants of growth and hydrolysis processes were not affected considerably.

Effect of photochemical treatment on the biocompatibility of a commercial nonionic surfactant used in the textile industry

The degradability of surfactants is a frequent and complex issue arising both at domestic as well as industrial treatment facilities. The present paper describes a laboratory study conducted to elucidate the photochemical and biochemical treatability of a nonionic, alkyl polyethylene ether-based surfactant formulation commonly used in the textile preparation stage. The application of H 2O 2/UV-C advanced photochemical oxidation appeared to be a suitable treatment alternative and 90% COD removal (COD 0≈500 mg/L) could be achieved under optimized process conditions. A significant COD removal efficiency (74%) could also be reached after biodegradation (final COD=135 mg/L) of the surfactant; however, necessitated an acclimation period of at least 6 weeks for the achievement of steady-state conditions. H 2O 2/UV-C treatment efficiency was seriously retarded upon elevation of the initial COD to around 1000 mg/L, resulting in 46% COD and 38% TOC removal after 120 min photochemical oxidation (H 2O 2,0=1020 mg/L; pH 0=9.1). The BOD 5/COD ratio increased from 0.23 to 0.31 after the application of H 2O 2/UV-C revealing that photochemical pretreatment may have a positive effect on the ultimate biodegradation of the nonionic surfactant. Although the time required for activated sludge treatment to reach steady-state conditions could be reduced to 3 weeks for the photochemically pretreated surfactant formulation biochemical COD removal efficiency dramatically decreased from 74% to 39% for the nonionic surfactant being subjected to H 2O 2/UV-C pretreatment (ultimate COD after activated sludge treatment=265 mg/L).

Combined Photochemical and Biological Processes for the Treatment of Linear Alkylbenzene Sulfonate in Water

In this study, the effects of photochemical pre-treatment (pilot-plant UV/H2O2 process) of linear alkylbenzene sulfonate (LAS) on its subsequent biological treatment were examined. It was observed that the photochemical pre-treatment of the LAS solution did not increase its biodegradability. Moreover, the effects of acclimated microorganisms on the biodegradability of the LAS solution were also studied. It was observed that the acclimated activated sludge increased the biodegradation of the LAS solution. However, due to the presence of some intermediates in the effluent of the photoreactor, the biodegradability of this effluent was less than the biodegradability of the untreated LAS solution with the same concentration of the LAS in the effluent of the photoreactor.

Treatment of atrazine by integrating photocatalytic and biological processes

This research examines the degradation of atrazine by photocatalytic oxidation (PCO) under different experimental conditions. Deisopropylatrazine, deethylatrazine and deethyldeisopropylatrazine were formed as major intermediates based on gas chromatography-mass spectrometry. The reaction mixture was found to be toxic towards two bioassays, i.e. the Microtox ® and amphipods survival tests even when atrazine was completely degraded by PCO within 2 h under optimized conditions. The results indicate that adding H 2O 2 could significantly enhance the degradation of atrazine by PCO. Ammeline, ammelide and cyanuric acid (CA) became the major intermediates/products as detected by high performance liquid chromatography from 6th to the 40th h of PCO treatment. After 72 h PCO treatment, only CA was detectable in the reaction mixture. Further degradation of CA was carried out by a newly isolated CA-degrading bacterium, Sphingomonas capsulata. The photochemical pretreatment integrated with microbial degradation lead to the complete degradation and detoxification of atrazine.

Treatment of atrazine by integrating photocatalytic and biological processes

This research examines the degradation of atrazine by photocatalytic oxidation (PCO) under different experimental conditions. Deisopropylatrazine, deethylatrazine and deethyldeisopropylatrazine were formed as major intermediates based on gas chromatography-mass spectrometry. The reaction mixture was found to be toxic towards two bioassays, i.e. the Microtox® and amphipods survival tests even when atrazine was completely degraded by PCO within 2 h under optimized conditions. The results indicate that adding H2O2 could significantly enhance the degradation of atrazine by PCO. Ammeline, ammelide and cyanuric acid (CA) became the major intermediates/products as detected by high performance liquid chromatography from 6th to the 40th h of PCO treatment. After 72 h PCO treatment, only CA was detectable in the reaction mixture. Further degradation of CA was carried out by a newly isolated CA-degrading bacterium, Sphingomonas capsulata. The photochemical pretreatment integrated with microbial degradation lead to the complete degradation and detoxification of atrazine.

Photoorientation of a Liquid-Crystalline Polyester with Azobenzene Side Groups: Effects of Irradiation with Linearly Polarized Red Light after Photochemical Pretreatment

In contrast to the conventional photoorientation process with blue light, an orientation of 4-cyano-4‘-alkoxyazobenzene side groups parallel to the electric field vector of the incident light is generated upon irradiating films of a liquid-crystalline side-chain polymer with linearly polarized red light. The polyester is characterized by smectic and nematic phases g24SX26SA34N46i and a strong tendency to form J-aggregates. The process requires a photochemical pretreatment by irradiation with UV light or an exposure to visible light of high power density to produce a certain concentration of the Z-isomer, which destroys any initial orientational order and J-aggregates. The orientation process is cooperative, whereas the light-induced orientation of the photochromic moiety causes an ordering of the alkylene spacers and even of the main-chain segments into the same direction. The most probable mechanism of this two-step process is the angular-selective transformation of the bulky Z-isomers to the rodlike E-isomeric formed by the red light. The aligned E-azobenzene side groups become strongly J-aggregated. Very high values of dichroism of about 0.8 and birefringence of about 0.3 were generated as a result of this combination of the photoinduced orientation process and the thermotropic self-organization, which take place simultaneously under the irradiation conditions. The process results in a uniaxial prolate order of the film, whereas conventional photoorientation leads to a biaxial oblate order. These two different three-dimensional orders have been characterized by FTIR polarization spectroscopy and exhibit also varying intermediate thermal stabilities.

Photo-orientation of azobenzene side chain polymers parallel or perpendicular tothe polarization of red HeNe light

The mechanism of the light-induced orientation process of azobenzene-containingpolymers caused by irradiation with linearly polarized red light is investigated.This process is surprising because there is almost no absorption at 633 nm.Depending on the photochemical pre-treatment and the exposure time,the azobenzene moieties can undergo two different orientation processesresulting in either a parallel or a perpendicular orientation with respect tothe electric field vector of the incident light. The fast orientation of thephotochromic groups with their long axis in the direction of the light polarizationrequires a photochemical pre-treatment in which non-polarized UV lightgenerates Z-isomers. Due to this procedure the film becomes ‘photochemicallyactivated’ for the subsequent polarized irradiation with red light. But oncontinued exposure a second, much slower reorientation process occurswhich establishes an orientation of the azobenzene groups perpendicular tothe electric field vector. The fast mechanism is probably caused by anangle-selective photo-isomerization of the Z-isomers to the E-isomers, whilethe subsequent slow reorientation process is caused by the well-knownconventional photo-orientation taking place via the accumulation of a number ofphotoselection steps and the rotational diffusion minimizing the absorbance of theE-isomer. This process occurs in the steady state but at this wavelengthwith a very small concentration of Z-isomers. The competing mechanismstake place in the same polymer film under almost identical irradiationconditions, differing only in the actual concentration of the Z-isomers.

Recent developments in the coupling of photoassisted and aerobic biological processes for the treatment of biorecalcitrant compounds

A general strategy to develop combined photochemical and biological system for biorecalcitrant wastewater treatment is proposed. For the development of this strategy, the following points were taken into account: the biodegradability of initial solutions, the operation mode of the coupled reactor, the chemical and biological characteristics of the phototreated solutions, the evaluation of different photoassisted advanced oxidation processes, the optimal conditions of both photochemical and biological processes, and the efficiency of the coupled reactor. The strategy to couple photochemical and biological processes is illustrated by case studies of four different biorecalcitrant pollutants. Three kinds of combined systems were developed using either photo-Fenton, Fe 3+/UV, or TiO 2 supported on glass rings for the photocatalytic pretreatment and in all cases immobilized biomass for the biological step. The advantages of the each coupled system are discussed and beneficial effects of such two-step treatments were found. However this strategy is not a universal solution. Chemical, biological, and kinetic studies must be always carried out to ensure that the photochemical pretreatment increase the biocompatibility of the treated wastewater. Some field experiments using solar reactor indicated that a coupled photochemical–biological treatment system at pilot scale is a possible way to achieve the complete mineralization of the biorecalcitrant pollutants.

Decolorization of reactive dyes by immobilized laccase

Immobilization of laccase by Trametes versicolor on silica chemically modified with imidazol groups, amberlite IRA-400, glass–ceramic chemically modified with carbodiimide/glutaraldehyde and by aminoprolyltriethoxysilane/glutaraldehyde and montmorillonite modified by aminoprolyltriethoxysilane/glutaraldehyde were afforded. These supports were used in the decolorization of textile reactive dyes (Remazol Brilliant Blue R, Remazol Black B, Reactive Orange 122 and Reactive Red 251). One of the most efficient supports was studied in a more detailed way, silica modified by imidazole SiIm led us to obtain almost total immobilization of laccase at contact times lower than 45min. The immobilized laccase showed high decolorization efficiency toward aqueous solutions of the dyes. In the first stages of the process, the decolorization is mainly due to adsorption of the dyes onto the support surface. However, when working in a successive dye addition system, the adsorption capacity of the supports decrease (saturation) and the enzymatic decolorization process is clearly evidenced. The use of a brief photochemical pre-treatment permitted a significantly increase on the efficiency of the enzymatic decolorization process.

Photo-Fenton treatment of a biorecalcitrant wastewater generated in textile activities: biodegradability of the photo-treated solution

Photo-Fenton process was explored as photochemical pre-treatment to improve the biodegradability of a wastewater coming from a textile industry located in the south of France, which was characterized as very biorecalcitrant by means of Zahn–Wellens biodegradability test. The effect of H2O2, Fe(III) and temperature on the photo-mineralization processes have been studied and the optimal conditions were found. Experiments were made to obtain information concerning the evolution of the biodegradability of the treated effluent after 40 and 70% of photo-mineralization. The photo-treated effluent is not biocompatible and its complete mineralization cannot be performed by biological means. UV–VIS and high-performance liquid chromatography (HPLC) analyses show that aromatic intermediates remain in the effluent after the photo-treatment, which have been identified as the principal reason of the biorecalcitrance.

Influence of Liquid Crystallinity and Aggregation on Photo-orientation

The dependence of the Photo-orientation process on the liquid crystallinity and the molecular aggregation is studied. In the case of ordered films the photo-orientation is restricted, but this restriction can be overcome by a photochemical pre-treatment using UV light or by higher power density of the incident Vis light. The optical anisotropy increases with spacer length or the ordering tendency of the polymers.

Biodegradation of Photoirradiated Polycyclic Aromatic Hydrocarbon Constituents of Creosote Oil

The influence of the photochemical pretreatment on the biodegradation of naphthalene, acenaphthene, fluorene, phenanthrene, anthracene, and pyrene were studied. In aqueous media these PAHs were photoreactive. Aerobic PAH degrading bacteria were enriched on creosote or on a mixture of the six PAHs. The pre-irradiation enhanced mainly the onset of the biodegradation, particularly PAHs treated as the components of creosote. The biodegradation rate of irradiated acenaphthene in creosote on the second day was 50% better than that in the non-irradiated sample. The biodegradation rates of anthracene irradiated individually and in creosote were 35% and 58% higher, respectively, than those of the non-irradiated samples on the second day. On the seventh day there was a 70% difference between the biodegradation rates of irradiated and non-irradiated pyrene treated in creosote in favor of the irradiated sample. The biodegradation of non-irradiated fluorene ceased in two days while the degradation of irradiated fluorene was almost complete in seven days. Photochemical treatment produced several intermediates as detected by a gas chromatograph with a mass spectrometer (GC-MS). The intermediates were more biodegradable than the parent compounds.

Chemical (photo-activated) coupled biological homogeneous degradation of p-nitro- o-toluene-sulfonic acid in a flow reactor

This study presents the combined photochemical (Fenton) and biological flow reactor degradation of p-nitrotoluene- ortho-sulfonic acid ( p-NTS). p-NTS is a compound whose degradation is not possible by waste water bacteria. From this point of view it is considered as a non-biodegradable intermediate found in the manufacture of dyes, surfuctants and brighteners. By way of HPLC technique it is shown that the photochemical pretreatment of p-NTS induces dearomatization due to -OH radical attack. A concomitant 20–25% decrease in the initial carbon content during the photochemical pretreatment was observed along the abatement of the aromaticity. This study shows that the intermediates produced in the pretreatment stage are biodegradable. After pretreatment a minimum residual H 2O 2 (< 0.2 mg l −1) was attained. This level of oxidant did not interfere with the subsequent biological degradation. The influence of the reaction parameters such as: input concentration of p-NTS, rate of H 2O 2 addition, reactor flow rate, TOC reduction rate and BOD 5/COD as a function of the time of photochemical pretreatment are reported. At a flow rate of 0.18 l h −1 (5.5. h residence time) a photochemical degradation efficiency of 75%, a biological degradation efficiency of 52% and an overall degradation efficiency for the coupled process of 88% was observed. The disappearance of p-NTS in the photochemical reactor, the growth and degradation of the benzoquinone like aromatic intermediate followed by the appearance short chain aliphatic compounds are reported as a function of pretreatment time. The increase in BOD/TOC as function of pretreatment time has been correlated to the p-NTS and aliphatic recalcitrants existing in the solution. The biological degradation was observed to be strongly dependent on the flow used and on the pollutant loading of the solution. These were the two main parameters affecting the degradation in the bioreactor.

Electrochemical versus photochemical pretreatment of industrial wastewaters

Electrochemical and photochemical treatments have been applied on industrial non-biodegradable effluents originated from a flavour manufacturing facility. The efficiency has been measured in each case. Such an approach has been used before successfully on model substances and is confirmed in the present study as a valid approach for industrial waste water. During electrochemical treatment, the values for the temperature, pH, electrode characteristics, initial concentration of effluents and NaCl used have been optimized through preliminary experiments. After a charge of 5 Ah/l the TOC observed decreased by 52% and the ratio TOC/COD decreased from 3.3 to 1.7. After electrochemical treatment and chlorine neutralization the effluents become easily biodegradable and no toxicity was observed. Photo-Fenton system under solar lamp have shown to be efficient in the photochemical degradation of industrial effluent when Fe3+-ion (4.3 mg in 40ml) and H2O2 (30μl/h in 40 ml) is added to the solution. After 10 hours a degradation of 56% of TOC was observed. The toxicity and biodegradability of pretreated wastewater were evaluated after having decomposed the residual H2O2 with catalase. Toxicity did not increase during photochemical treatment but the biodegradability strongly increased.

Electrochemical versus photochemical pretreatment of industrial wastewaters

Electrochemical and photochemical treatments have been applied on industrial non-biodegradable effluents originated from a flavour manufacturing facility. The efficiency has been measured in each case. Such an approach has been used before successfully on model substances and is confirmed in the present study as a valid approach for industrial waste water. During electrochemical treatment, the values for the temperature, pH, electrode characteristics, initial concentration of effluents and NaCl used have been optimized through preliminary experiments. After a charge of 5 Ah/l the TOC observed decreased by 52% and the ratio TOCICOD decreased from 3.3 to 1.7. After electrochemical treatment and chlorine neutralization the effluents become easily biodegradable and no toxicity was observed. Photo-Fenton system under solar lamp have shown to be efficient in the photochemical degradation of industrial effluent when Fe3+-ion (4.3 mg in 40ml) and H2O2 (30μ1/h in 40 ml) is added to the solution. After 10 hours a degradation of 56% of TOC was observed. The toxicity and biodegradability of pretreated wastewater were evaluated after having decomposed the residual HH2O2 with catalase. Toxicity did not increase during photochemical treatment but the biodegradability strongly increased.

Vuv‐Photolysis. oxidative degradation of organics inhibiting the inverse‐Voltammetric determination of heavy metals. 1. Humic substances

Abstract A Xe‐excimer lamp (irradiation wavelength 172 ± 12 nm) was used to examine pretreatment of samples to be analyzed by stripping anodic voltammetry to eliminate complex formation of metal ions with organic substances which severely affect the quantitative analysis of heavy metals. VUV irradiation provides complete and fast oxidative degradation of e.g. humic substances without addition of oxidizing reagents except air. The result of the photochemical pretreatment is demonstrated in comparative analyses of mixtures of Pb2+, Cd2+, Cu2+ and In3∗ ions.

Biomass photochemistry: XII. Chemical and photochemical pretreatment of rice hull and its fungal degradation

Biomass photochemistry: XII. Chemical and photochemical pretreatment of rice hull and its fungal degradation